I have tested it syncs reliably with over 1500 entries. Will continue to pump those numbers up until something breaks.
Discussion
Have now tested syncing 2200 entries across multiple nostr relays reliably cross platforms.
Worth noting that sensitive information is never stored anywhere on disk or nostr. It's always deterministically generated based on the seed. The associated information like index number, label and URL etc. is what gets synced across nostr.
